The present invention relates to rotational flux conduction in thin film magnetic devices.
Magnetic devices, such as thin film recording heads, whether read, read/write, or write, are designed to have particular magnetic orientations, or domains, within the active regions of the device material. The static state of each of these domains can be oriented along a given axis, known as the easy axis (or axis of anisotropy), as desired, by control of the manufacturing process. Performance is critically linked to domain formation, and, therefore, control can be exerted over device performance by controlling domain formation.
Conduction of flux, such as in a thin film recording head, is achieved by two mechanisms: domain wall motion and domain rotation. Domain wall motion results in flux being transmitted through a thin film head along the walls of a domain, or domains, the flux spreading out along the domain walls as the flux seeks to return to equilibrium. However, while domain wall motion facilitates conduction of flux at low frequencies, it is a poor vehicle for conduction of flux at high frequencies. Furthermore, defects in the material in a magnetic head can be the source of Barkhausen noise during conduction of flux by wall motion as the flux is perturbed by these defects. Such noise can result in erroneous readings of recorded data.
A conventional prior art pole of a magnetic recording head is shown in FIG. 1(a), where medium M will be seen as inserting signal flux into a first transversely oriented domain dl of a series of transversely oriented domains dl-dn. The rest state flux of the domains is in the X-axis (transverse direction), which leaves a rotational option of flowing into the Y axis (longitudinal direction) or Z axis (vertical direction) in reaction to the signal flux from the medium. The Z-axis is out of plane and is a high reluctance path. Hence the flux will rotate into the Y-axis, as indicated by the rotated arrows of each of domains dl-dn.
In view of the foregoing, it will be understood that conduction of flux by domain rotation may be achieved by configuring a series of neighboring transverse domains axially aligned along parallel axes, where signal flux impinged upon the first domain at a given angle will cause the magnetization of that domain to rotate from its static orientation by that angle radially into and impinging upon the neighboring domain. Such rotation can be transmitted in a like manner along an axis of flux transmission by each neighboring domain of the series. Hence, flux can be conducted in the pole and through the yoke of a thin film head in a series of domain rotations. The yoke enables conduction of flux through a transducer which produces electrical signals proportional to flux levels or the rate of flux change. The transducer might be an induction coil or other flux sensing device. An induction coil is shown schematically in FIG. 1(a) as it might overlie the bottom pole of a two pole structure.
Further discussion of the flux conduction mechanisms will be found in co-pending patent application entitled: "Perpendicular Anisotropy In Thin Film Devices", U.S. Ser. No. 07/227,813, filed Aug. 3, 1988, which is incorporated herein by reference.